Journal of Postgraduate Gynecology & Obstetrics is an Open Access, peer reviewed online journal published by Department of Obstetrics and Gynecology of Seth G. S. Medical College and K.E.M. Hospital, Parel, Mumbai, 400012, India.

High Dose Hook Effect With Urine Pregnancy Test

Urine pregnancy test (UPT) kits are widely used for qualitative β human chorionic gonadotropin assay (hCG). We report a case where false negative UPT was caused by high dose “hook effect” due to gestational trophoblastic neoplasia (GTN), leading to delay in diagnosis.

Introduction

UPT kits are used as one step point- of- care test for the detection of β hCG in urine to confirm pregnancy. However false negative and false positive tests are seen, though rarely.[1] β hCG secreting tumors can result in false positive or negative test results. Any false results can delay the diagnosis and precipitate complications.

Case Report

A 28 year old lady married since 2 years with previous 2 ectopic pregnancies and no living issue was referred with complaints of pain in abdomen and vomiting since 1 week. She had bleeding per vaginum 5 days back. She was a diagnosed case of polycystic ovarian disease. Her menstrual cycles were irregular. Laparoscopic removal of right ovarian ectopic pregnancy ( preoperative β hCG-8299 mIU/ml ) was done 7 months back and was confirmed on histopathological examination. No follow up β hCG reports were available for a period of 6 months. After 6 months, on the basis of four consecutive β hCG values ( 13170, 53880, 74400 , 10345 mIU/ ml) and laparoscopic findings; omental ectopic pregnancy was removed and confirmed on histopathology examination. On follow up, β hCG values were 3232, 173544, 2360 mIU/ml over a period of 1 month and then the patient was referred to our hospital for further management.

On examination, she had tachycardia and pallor. Her abdomen was mildly distended and tender; ill defined cystic mass was felt corresponding to 16 weeks uterine size. On per vaginal examination 10 x 10 cm cystic, tender mass was felt. Right anterior and lateral forniceal fullness was felt. Uterus was not felt separately from the mass. Cervical os was closed and there was no bleeding. Ultrasonography showed hypoechoic mass in the right iliac fossa measuring 11 x 6 x 8 cm with mild vascularity with arterial and venous flow. Both ovaries were enlarged in size and showed multiple cysts within. Uterus was normal in size. Moderate free fluid with echoes was present in the pouch of Douglas suggestive of hemoperitoneum. There was a hyperechoic lesion in segment VI of liver suggestive of hemangioma. Provisional diagnosis of ovarian cyst with torsion, or ovarian hyperstimulation syndrome or GTN was made. β hCG, tumor markers and UPT was done. Serum LDH was 1214 U/ ml. Serum β hCG levels were > 2,60,000 mIU/ ml, but her UPT was negative.

In view of the high serum β hCG values, but in view of negative UPT, false negative qualitative β hCG test was suspected in our case. Hence we diluted the urine sample in 1:5 ratio with normal saline and repeated the test using the standard UPT kit. The test then showed a positive result. The dilution step confirmed the high dose hook effect in this case. On further investigations, the diagnosis of gestational trophoblastic neoplasia with liver metastasis was confirmed and patient was referred to the cancer institute for further management (chemotherapy).

Discussion

UPT kits employ monoclonal antibodies or a combination of monoclonal and polyclonal antibodies and are called the sandwich assays. β subunit is measured in pregnancy tests. These assays consist of fixed solid phase antibody attached to matrix and a separate free or soluble antibody attached to a reporter label. Sandwich is formed as antibodies bind to different epitopes of hCG and signal is visualized as a positive test.[2] Failure to detect urine hCG can occur due to excess amount of hCG. High dose hook effect is seen at beta hCG levels > 1,000,000 mIU/ ml as seen in gestational trophoblastic disease. Excessive hCG saturates fixed solid phase antibody and labeled soluble antibody and formation of sandwich is prevented. This results in the absence of signal and the reader reads the test as negative.[3] When high dose hook effect is suspected, urine sample needs to be diluted to reduce the concentration of hCG. A high dose hook effect is confirmed if test becomes positive after diluting the sample.[4]